1. Field of the Invention
The invention relates to displacement machines for compressible mediums, with several spiral-shaped conveying spaces which are disposed in a stationary housing and which lead from an inlet lying radially on the outside, to an outlet lying radially on the inside. A displacement body which is assigned to the conveying spaces, comprises a disk with spiral-shaped strips arranged perpendicularly on both sides. The displacement body, driven off-centered, is made of a magnesium alloy, and during service each of its points affects a circular movement defined by the circumferential walls of the conveying space.
2. Discussion of the Background
Displacement machines of the spiral design are known from DE-C-26 03 462. A compressor built according to this principle provides an almost pulsation free conveying of the gaseous working medium, which consists of, for example, air or a mixture of air and fuel. It could also be used advantageously for charging internal combustion engines. While such a compressor is operating, several crescent-shaped working spaces, which move from the inlet through the displacement chamber to the outlet, are enveloped along the displacement chamber between the spiral-shaped displacement body and the two circumferential walls of the displacement chamber.
A machine of the aforementioned type is known from the EP-A-0 354 342. To better utilize the volume of the machine, the trend of development is in the direction of higher pressure ratios and higher speeds. The former causes steeper temperature gradients in the disk; the latter leads to greater inertial forces. Therefore, the displacement body is made preferably of a light metal alloy, for example magnesium. Thus, the inertial forces acting on the main eccentric bearing can be minimized. The two halves of the housing of such a machine are usually made of an inexpensive aluminum die casting. With suitable rigid construction of the drive shaft and the bearing part of the rotor, this pairing of the material the spiral walls of the displacement body and the housing ribs can permit touch contact in the circumferential direction of the spiral. The materials wear to produce zero play without galling of one of the elements involved. The result is a greater tolerance owing to the mechanical treatment of the elements and higher operating temperatures of the machine during service.